Methods of synthesizing heteroatom-bearing ligands and intermediate used therefor

ABSTRACT

The invention provides improved and simplified methods of synthesizing ligands containing a heteroatom-bearing bridge using a novel intermediate compound. The ligands may be used to form metal complexes that are useful in diagnostic and therapeutic applications.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of and claims priority from U.S.patent application Ser. No. 09/818,301, filed Mar. 27, 2001.

FIELD OF THE INVENTION

[0002] The present invention relates to compounds containing aheteroatom-bearing bridge, and to complexes of these compounds withmetals. In particular, the invention relates to improved and simplifiedmethods of synthesizing such compounds using a novel intermediate.

BACKGROUND OF THE INVENTION

[0003] Metal complexes, such as those containing radioactive metals, areuseful as diagnostic and therapeutic agents. Complexes containingbioactive moieties capable of being selectively taken up at a desiredsite to facilitate evaluation or treatment of a subject are ofparticular interest. For example, U.S. Pat. No. 5,608,110 disclosescompounds containing a heteroatom-bearing bridge which may be complexedwith a metal and used in diagnostic and therapeutic methods. AlthoughU.S. Pat. No. 5,741,912 discloses methods for preparing a variety ofsuch compounds, there remains a need for simplified methods ofsynthesizing these compounds. The present invention addresses the needin the art for improved and simplified methods of synthesizing ligandsfor use in metal complexes, particularly complexes containinghypoxia-localizing moieties.

SUMMARY OF THE INVENTION

[0004] The present invention features methods of making compounds, alsoreferred to herein as ligands, using a novel intermediate. Inparticular, the invention features improved and simplified methods ofmaking compounds having the structure of Formula I:

[0005] where all R and R* groups are independently:

[0006] (i) R²;

[0007] (ii) halogen, especially fluoro;

[0008] (iii) —OR²;

[0009] (iv) —C(O)—OR²;

[0010] (v) —C(O)—N(R²)₂;

[0011] (vi) —N(R²)₂;

[0012] (vii) -alkyl-C(O)—OR²;

[0013] (viii) -alkyl-C(O)—N(R²)₂;

[0014] (ix) -alkyl-N(R²)₂;

[0015] (x) -aryl-C(O)—OR²;

[0016] (xi) -aryl-C(O)—N(R²)₂;

[0017] (xii) -aryl-N(R²)₂;

[0018] (xiii) acyl;

[0019] (xiv) acyloxy;

[0020] (xv) heterocyclo;

[0021] (xvi) hydroxyalkyl;

[0022] (xvii) —SO₂—R²;

[0023] (xviii) -alkyl-SO₂—R²;

[0024] (xix) —(A)_(p)—R³, where A is a linking group, p is 0 or apositive integer, and R³ is a bioactive moiety; or

[0025] (xx) two R groups, or an R group and an R* group, taken togetherwith the one or more atoms to which they are bonded, form a saturated orunsaturated, spiro or fused, carbocyclic (such as fused 1,2-phenyl) orheterocyclic ring which may be unsubstituted or substituted by one ormore groups selected from the groups (i) to (xix) above;

[0026] with the proviso that a carbon atom bearing an R group is notdirectly bonded to more than one heteroatom; and

[0027] R² is independently hydrogen, alkyl, alkenyl, alkynyl, or aryl.

[0028] The synthetic method of the invention provides compounds ofFormula I through the following novel intermediate compound (FormulaII):

[0029] In the synthetic scheme of the present invention, theintermediate compound of Formula II may be isolated and purified. Thesynthetic method of the invention also provides stereoisomers of theintermediate compound, such as2-{(1R)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione:

[0030] and2-{(1S)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione:

[0031] The intermediate compound of Formula II may also be used to makea variety of compounds of Formula I. Preferred compounds are obtained byfirst reacting the intermediate of Formula II with hydrazine of theformula:

NH₂—NH₂

[0032] to yield 1-[3-amino-2-(aminooxy)propyl]-2-nitro-1H-imidazoledihydrochloride, which is then reacted with a compound of Formula III.Compounds of Formula III may include compounds of Formula IIIa orFormula IIIb, set forth below, or a mixture of these two compounds:

[0033] where X is halogen (preferably Cl, Br or I) and R and R* aredefined above, to yield a compound of Formula I. A preferred compound ofFormula III is 3-chloro-3-methyl-2-nitrosobutane.

[0034] A preferred compound of Formula I is compound Ia,3,3,9,9-tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dione dioxime:

[0035] The invention also provides methods of synthesizing stereoisomersof compound Ia, such as(S)-(−)-3,3,9,9-tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime:

[0036] andR-(−)-3,3,9,9-tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime:

[0037] Compounds of Formula I may be complexed with metals, preferablyradioactive metals discussed below, such as rhenium or technetium, andused in diagnostic and therapeutic methods. Compounds of Formula I arederivatized with a 2-nitro-imidazole hypoxia-localizing moiety. Thishypoxia-localizing moiety retains the biochemical behavior and affinityof the free moiety. Compounds of Formula I are capable of rapidlyproviding increased amounts of a desired radionuclide selectively totargeted areas, may be labeled at ambient temperature with suitableradionuclides, and are membrane permeable, allowing intracellulardelivery. Compounds of Formula I may include one or more additionalbioactive moieties.

[0038] As discussed in more detail below, the novel synthetic methoddisclosed herein is improved over the previously available methods inthat it is simpler and provides better yields than those previouslyavailable.

DETAILED DESCRIPTION

[0039] Definitions

[0040] The following definitions apply to the terms as they are usedthroughout the specification, unless otherwise indicated.

[0041] The terms “alkyl” or “alk,” as used herein alone or as part ofanother group, denote optionally substituted, straight and branchedchain saturated hydrocarbon groups, preferably having 1 to 12 carbons inthe normal chain, most preferably lower alkyl groups. Exemplaryunsubstituted groups include methyl, ethyl, propyl, isopropyl, n-butyl,t-butyl, isobutyl, pentyl, hexyl, isohexyl, heptyl, 4,4-dimethylpentyl,octyl, 2,2,4-trimethylpentyl, nonyl, decyl, undecyl, dodecyl and thelike. Exemplary substituents include one or more of the followinggroups: halo, alkoxy, arylalkyloxy (e.g., benzyloxy), alkylthio,alkenyl, alkynyl, aryl, cycloalkyl, cycloalkenyl, hydroxy, carboxyl(—COOH), amino, alkylamino, dialkylamino, formyl, alkylcarbonyloxy,alkylcarbonyl, heterocyclo, aryloxy or thiol (—SH). Preferred alkylgroups are unsubstituted alkyl, haloalkyl, arylalkyl, aminoalkyl,alkylaminoalkyl, dialkylaminoalkyl, alkyloxyalkyl, aryloxyalkyl,hydroxyalkyl and alkoxyalkyl groups.

[0042] The terms “lower alk” or “lower alkyl,” as used herein, denotesuch optionally substituted groups as described above for alkyl having 1to 4 carbon atoms in the normal chain.

[0043] The terms “alkoxy” or “alkylthio” denote an alkyl group asdescribed above bonded through an oxygen linkage (—O—) or a sulfurlinkage (—S—), respectively. The term “alkylcarbonyl,” as used herein,denotes an alkyl group bonded through a carbonyl group. The term“alkylcarbonyloxy,” as used herein, denotes an alkyl group bondedthrough a carbonyl group which is, in turn, bonded through an oxygenlinkage.

[0044] The term “alkenyl,” as used herein alone or as part of anothergroup, denotes optionally substituted, straight and branched chainhydrocarbon groups containing at least one carbon to carbon double bondin the chain, and preferably having 2 to 10 carbons in the normal chain.Exemplary unsubstituted such groups include ethenyl, propenyl, butenyl,pentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, and the like.Exemplary substituents include one or more alkyl groups as describedabove, and/or one or more groups described above as alkyl substituents.

[0045] The term “alkynyl,” as used herein alone or as part of anothergroup, denotes optionally substituted, straight and branched chainhydrocarbon groups containing at least one carbon to carbon triple bondin the chain, and preferably having 2 to 10 carbons in the normal chain.Exemplary unsubstituted such groups include ethynyl, propynyl, butynyl,pentynyl, hexynyl, heptynyl, octynyl, nonynyl, decynyl, and the like.Exemplary substituents include one or more alkyl groups as describedabove, and/or one or more groups described above as alkyl substituents.

[0046] The term “cycloalkyl,” as used herein alone or as part of anothergroup, denotes optionally substituted, saturated cyclic hydrocarbon ringsystems, preferably containing 1 to 3 rings and 3 to 7 carbons per ring.Exemplary unsubstituted such groups include cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclodecyl,cyclododecyl, and adamantyl. Exemplary substituents include one or morealkyl groups as described above, and/or one or more groups describedabove as alkyl substituents.

[0047] The abbreviation “DEAD” refers to diethylazodicarboxylate.

[0048] The term “cycloalkenyl,” as used herein alone or as part ofanother group, denotes such optionally substituted groups as describedabove for cycloalkyl, further containing at least one carbon to carbondouble bond forming a partially unsaturated ring. Exemplary substituentsinclude one or more alkyl groups as described above, and/or one or moregroups described above as alkyl substituents.

[0049] The terms “ar” or “aryl,” as used herein alone or as part ofanother group, denote optionally substituted, homocyclic aromaticgroups, preferably containing 1 or 2 rings and 6 to 12 ring carbons.Exemplary unsubstituted such groups include phenyl, biphenyl, andnaphthyl. Exemplary substituents include one or more, preferably threeor fewer, nitro groups, alkyl groups as described above and/or groupsdescribed above as alkyl substituents. Preferred aryl groups areunsubstituted aryl and hydroxyaryl.

[0050] The term “carbocyclic,” as used herein alone or as part ofanother group, denotes optionally substituted saturated, partiallyunsaturated or aromatic homocyclic hydrocarbon ring systems such as thecycloalkyl, cycloalkenyl or aryl groups described above.

[0051] The terms “heterocyclo” or “heterocyclic,” as used herein aloneor as part of another group, denote optionally substituted fullysaturated or unsaturated, aromatic or non-aromatic cyclic groups havingat least one heteroatom in at least one ring, preferably monocyclic orbicyclic groups having 5 or 6 atoms in each ring. The heterocyclo groupmay, for example, have 1 or 2 oxygen atoms, 1 or 2 sulfur atoms, and/or1 to 4 nitrogen atoms in the ring. Each heterocyclo group may be bondedthrough any carbon or heteroatom of the ring system. Preferred groupsinclude those of the following formula, which may be bonded through anyatom of the ring system:

[0052] where r is 0 or 1 and T is —O—, —S—, —N—R⁸ or —CH—R⁸ where R⁸ ishydrogen, alkyl, aryl or arylalkyl. Exemplary heterocyclo groups includethe following: thienyl, furyl, pyrrolyl, pyridyl, imidazolyl,pyrrolidinyl, piperidinyl, azepinyl, indolyl, isoindolyl, quinolinyl,isoquinolinyl, benzothiazolyl, benzoxazolyl, benzimidazolyl,morpholinyl, piperazinyl, 4-alkylpiperazinyl, 4-alkylpiperidinyl,3-alkylpyrrolidinyl, oxazolyl, pyrazolyl, thiophenyl, pyridazinyl,thiazolyl, triazolyl, pyrimidinyl, 1,4-dioxanyl, benzoxadiazolyl, andbenzofuranyl. Exemplary substituents include one or more alkyl groups asdescribed above and/or one or more groups described above as alkylsubstituents.

[0053] The terms “halogen,” “halo,” or “hal,” as used herein alone or aspart of another group, denote chlorine, bromine, fluorine, and iodine.

[0054] The term “acyl,” as used herein alone or as part of anothergroup, denotes the moiety formed by removal of the hydroxyl group fromthe group —COOH of an organic carboxylic acid. Exemplary such groupsinclude alkylcarbonyl, arylcarbonyl, or carbocyclo- orheterocyclocarbonyl. The term “acyloxy,” as used herein alone or as partof another group, denotes an acyl group as described above bondedthrough an oxygen linkage (—O—).

[0055] For the above optionally substituted groups, reference to aspecific substituent may be made without excluding the presence of othersubstituents. Thus, for example, “hydroxyalkyl” is a straight orbranched chain saturated hydrocarbon group bearing at least one hydroxysubstituent and no other or, optionally, one or more additional,substituents.

[0056] The terms “bioactive group” or “bioactive moiety,” as usedherein, denote a group which is capable of functioning as a metabolicsubstrate, catalyst, or inhibitor, or is capable of being preferentiallytaken up at a selected site of a subject, such as by possessing anaffinity for a cellular recognition site. Compounds produced by themethod disclosed herein contain at least one bioactive group, a hypoxialocalizing moiety.

[0057] The terms “hypoxia localizing group” or “hypoxia localizingmoiety”, as used herein denote a specific bioactive group or moietywhich is capable of specifically localizing in hypoxic tissue (e.g.tissue which is deficient in oxygen, but still viable). Suitable hypoxialocalizing moieties are those which are preferentially retained inregions of a subject which are hypoxic relative to the degree ofretention in tissues which are normoxic. Compounds produced by themethod disclosed herein contain at least one hypoxia localizing moiety.

[0058] The term “linking group,” as used herein, denotes a group which,alone or together with one or more other groups, may be used tocovalently bond a bioactive group to the remainder of a compound ofFormula I.

[0059] The various substituents of the ligands of the present inventionmay be chosen to form stable compounds.

[0060] Synthesis of Compounds of Formula I

[0061] The synthetic method of the invention is illustrated in thefollowing General Reaction Scheme and in the Example herein.

[0062] According to the General Reaction Scheme,N-(2,3-epoxypropyl)phthalimide (1) is reacted with 2-nitro-imidazole (2)to obtain2-[2-Hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione(3). This product is then reacted with N-hydroxyphthalimide, preferablyin the presence of a tertiary amine such as triphenylphosphine, toobtain the intermediate of Formula II,2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione(4). This intermediate is then reacted with hydrazine to obtain1-[3-amino-2-(aminooxy)propyl]-2-nitro-1H-imidazole dihydrochloride (5),which is then reacted with the compound of Formula III to yield thecompound of Formula I. A preferred compound of Formula III is3-chloro-3-methyl-2-nitrosobutane, which, when used contacted with1-[3-amino-2-(aminooxy)propyl]-2-nitro-1H-imidazole dihydrochloride (5),yields3,3,9,9-tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime (7).

[0063] Compounds of the Formula III may be prepared by methods such asthose described in Vassian, Inorg. Chem., 6, 2043-2046 (1967),Pfleiderer et al., Liebigs Ann. Chem., 99, 3008 (1966), or, especiallywhere R or R* is CH₃—, by the method of Nowotnik et al., European PatentNo. 0179608 A2 (1986).

[0064] This novel synthetic method provides distinct advantages overpreviously available methods. For instance, the method simplifies thesynthesis with a concomitant reduction in the number of steps necessaryto produce the compounds of Formula I. Specifically, the two secondaryamines of the novel intermediate of Formula II are both protected asphthalimides, which leads to fewer synthetic steps and higher yield.Unexpectedly, the intermediate of Formula II provides a solubilityprofile that allows simple extraction to remove impurities, which isexperimentally easier than the recrystallization or columnchromatography required by previously available methods. Thus, unlikemethods that require column chromatography, the synthetic methoddisclosed herein facilitates large scale synthesis. Additionally, thelast step of the synthesis provides a crystalline product and the newexperimental features HPLC monitoring of reagents for better control ofreaction. In short, the synthetic method disclosed herein is simpler andmore efficient than those previously available.

[0065] Metal Complexes

[0066] The compounds of Formula I may be employed as ligands for theformation of metal complexes. Metal complexes may be formed bycomplexing a ligand made using the synthetic method of the inventionwith a radioactive or non-radioactive metal, including metals having anatomic number 22-31, 39-49 or 73-82, especially a radioactive metal,preferably under basic conditions.

[0067] Preferred metal complexes are those in which a compound ofFormula I is complexed with a radioactive metal, such as technetium orrhenium, most preferably with technetium. Ligands which form single,neutral complexes are preferred. Exemplary complexes include thosehaving the following structure:

[0068] where M is technetium and R and R* are methyl. These metalcomplexes find utility as diagnostic and/or therapeutic agents. Themetal complexes of the present invention may be administered by anyappropriate route such as orally, parenterally (for example,intravenously, intraperitoneally, intramuscularly, or subcutaneously),or by any other suitable method. For example, the complexes of thisinvention may be administered to a subject by bolus or slow infusionintravenous injection.

[0069] The amount administered may be selected based on the desired use,such as to produce a diagnostic image of an organ or other site of asubject or a desired radiotherapeutic effect, by methods known in theart. Exemplary dosages are those employing about 30-200 mCi rhenium (forradiotherapy) or about 10-60 mCi technetium (for imaging). The “subject”of the methods of the present invention is preferably a mammal such as adomestic mammal, for example, a dog, cat, horse or the like, or mostpreferably, a human. Depending upon the metal and ligand used, thecomplexes of the present invention may be employed as, for example,imaging agents useful for imaging organs such as the heart, brain (wherethe complex may cross the blood-brain barrier), or the hepatobiliarysystem. They are especially useful for the imaging of hypoxic tissue,and as therapeutic agents, especially as hypoxic tissue cytotoxins, orradiosensitizers.

[0070] An exemplary method for the formation of a metal complex withligands made from the synthetic method of the present invention is thatwhere a complex or salt of the desired metal in the desired oxidationstate and containing one or more easily displaceable (i.e. labile)ligands (for example, H₂O, halogen (e.g. Cl), NO₃ ⁻, or sugars) is mixedwith ligand(s) at a pH value suitable for forming the desired complex.The labile ligand is displaced from the metal by the ligand(s) of thepresent invention to form a metal complex.

[0071] Illustrative such methods are shown as follows:

(Met)(Lig_(lab))4+(Lig_(inv))→(Met)(Lig_(inv))+4(Lig_(lab))  (1)

[0072] where

[0073] Met is a metal in a desired oxidation state;

[0074] Lig_(lab) is a labile ligand such as H₂O, Cl⁻, Br⁻, F⁻ or NO₃ ⁻;and

[0075] Lig_(inv) is a ligand made from the synthetic method of theinvention.

(Met)OCl₄ ⁻+(Lig_(inv))→(Met)O(Lig_(inv))+4Cl⁻  (2)

(Met)O₂(Lig_(mono))₄+(Lig_(inv))→(Met)O₂(Lig_(inv))+4(Lig_(mono))  (3)

[0076] where Lig_(mono) is a monodentate ligand such as pyridine,halide, phosphine or amine.

(Met)(Lig_(bi))₂+(Lig_(inv))→(Met)(Lig_(inv))+2(Lig_(bi))  (4)

[0077] or

(Met)O(Lig_(bi))₂+(Lig_(inv))→(Met)O(Lig_(inv))+2(Lig_(bi))  (5)

[0078] where Lig_(bi) is a bidentate ligand such as a sugar, a diol, abisamine, bipyridine or phosphine, and where, for each equation (1) to(5) above, the appropriate charge balance is employed.

[0079] Alternatively, metal complexes may be prepared from a metal in anoxidation state different from that of the desired complex. An exemplarysuch method is that where either a reducing agent or an oxidizing agent(depending on the oxidation state of the metal used, and the oxidationstate of the desired final product) is added to the reaction mixturecontaining metal to bring the metal to the desired oxidation state. Theoxidant or reductant may be used to form an intermediate complex in thedesired oxidation state but with labile ligands which are then displacedby a desired chelating ligand of the present invention; or the oxidantor reductant may be added to the reaction mixture containing metal alongwith the desired ligand to achieve the change to the desired oxidationstate and chelation to the desired metal in a single step.

[0080] Rhenium complexes are particularly useful in radiotherapy agents.The rhenium employed is preferably one of the radionuclides Re-186 orRe-188, or a mixture thereof, which mixture may also include Re-185and/or Re-187. Preparation of the complexes of the present inventionwhere the metal is rhenium may be accomplished using rhenium in the +5or +7 oxidation state. Examples of compounds in which rhenium is in theRe(VII) state are NH₄ReO₄ or KReO₄. Re(V) is available as, for example,[ReOCl₄](NBu₄), [ReOCl₄](AsPh₄), ReOCl₃(PPh₃)₂ and as ReO₂(pyridine)₄ ⁺.(Ph is phenyl; Bu is n-butyl). Other rhenium reagents capable of forminga rhenium complex may also be used. The use of “carrier rhenium” ispreferred. The phrase “carrier rhenium” means that the rhenium compoundsused contain non-radioactive rhenium at concentrations>10⁻⁷ M.

[0081] Technetium complexes are particularly useful in radiodiagnosticimaging agents. The technetium employed is preferably one or more of theradionuclides ^(99m)Tc, ^(94m)Tc or ⁹⁶Tc—. The preferred radioisotopefor medical imaging is ^(99m)Tc. Its 140 keV γ-photon is ideal for usewith widely available gamma cameras. It has a short (6 hour) half-life,which is desirable when considering patient dosimetry. ^(99m)Tc isreadily available at relatively low cost through commercially produced⁹⁹Mo/^(99m)Tc generator systems. Preparation of the complexes of thisinvention where the metal is technetium may be accomplished usingtechnetium in the form of the pertechnetate ion. For ^(99m)Tc, thepertechnetate ion is preferably obtained from commercially availabletechnetium-99m parent-daughter generators; such technetium is in the +7oxidation state. The generation of the pertechnetate ion using this typeof generator is well known in the art, and is described in more detailin U.S. Pat. Nos. 3,369,121 and 3,920,995. These generators maygenerally be eluted with saline solution, and the pertechnetate ionobtained as the sodium salt. Pertechnetate may also be prepared fromcyclotron-produced radioactive technetium using procedures well known inthe art.

[0082] The formation of a technetium complex is preferably achieved bymixing pertechnetate ion in normal saline with the appropriate ligand,preferably a ligand of Formula I. An appropriate buffer orphysiologically acceptable acid or base may be used to adjust the pH toa value suitable for labeling the ligand. This appropriate value of pHwill vary depending upon the nature of the ligand; for example, forligands of Formula I, a pH in the range between approximately equal to5.5 to approximately equal to 9.5 is suitable, preferably a pH value inthe range of 7.0 to 8.5. A source of reducing agent may then be added tobring the pertechnetate down to the oxidation state of Tc(V) forchelation with the ligand. Stannous ion is the preferred reducing agent,and may be introduced in the form of a stannous salt such as stannouschloride, stannous fluoride, stannous tartrate, stannousdiethylenetriamine pentaacetic acid (stannous DTPA), or stannouscitrate, or the like. The reaction is preferably run in an aqueous oraqueous/alcohol mixture, at or about room temperature, using a reactiontime of about 1 minute to about 1 hour. The reducing agent is preferablypresent at a concentration of 5 to 50 μg/mL. The ligand is preferablypresent in a concentration of 0.5 to 2 mg/mL. Optionally, co-ligands maybe added.

[0083] Alternatively, the technetium complexes produced from ligandsmade by the synthetic method of the invention may be prepared by ligandexchange. A labile Tc(V) complex may be prepared by the reduction ofTcO₄ ⁻ in the presence of a ligand which forms a labile technetiumcomplex, such as ethylene glycol, mannitol, or the hydroxy-carboxylateligands glucoheptonate, gluconate, citrate, malate or tartrate, at a pHvalue which is appropriate for the exchange ligand employed (usually 5to 8). A reducing agent, such as the stannous salts described above, maybe added, causing the formation of a labile reduced complex of Tc withthe exchange ligand. This reduced Tc complex is then mixed with theligand of Formula I at an appropriate pH value (as described above). Thelabile exchange ligand is displaced from the metal by the desiredligand, thus forming the technetium complexes of this invention.

[0084] Bioactive Moieties

[0085] A bioactive group as used herein is capable of functioning as ametabolic substrate, catalyst or inhibitor, for example, to aid inclearance of the complex from non-target tissue; or is capable of beingpreferentially taken up at a selected site of a subject, such as bypossessing an affinity for a cellular recognition site such as areceptor, enzyme, or transport mechanism, or by containing reactivegroups for coupling to proteins, or tissue localization by anotherbiochemical process. Thus, complexes of the present invention arecontemplated where one or more bioactive groups are bound to theremainder of the complex, such that the one or more bioactive groupsretain their desired bioactivity when so bound.

[0086] Exemplary bioactive groups include amphetamines, barbiturates,sulfonamides, monoamine oxidase substrates and inhibitors, hormones,enzymes, lipids, ligands for cell membrane receptors, antihypertensives,neurotransmitters, amino acids and oligopeptides, radiosensitizers,steroids (such as estrogen or estradiol),interchelators, monoclonal orpolyclonal antibodies or fragments thereof, sugars (such as glucosederivatives), fatty acids, substrates for muscarinic receptors (such as3-quinuclidinyl benzilate), substrates for dopamine receptors (such asspiperone), biotin, chemotactic peptides, substrates for benzodiazepinereceptors and, especially, hypoxia-localizing moieties described furtherbelow.

[0087] Examples of diagnostic uses for the complexes prepared by thesynthetic method of the invention include, but are not limited to,imaging of hypoxic tissue, e.g., in the heart, brain, lungs or intumors, preferably where the complexes contain a nitro-heterocyclicgroup trapped by hypoxia-mediated reduction of the nitro moiety(referred to herein as a “hypoxia-mediated nitro-heterocyclic group”),discussed further below; imaging of the brain and lungs when thebioactive group is a lipophilic amine-containing compound, e.g. anamphetamine; imaging of the brain, heart or tumors when the bioactivegroup is a sugar (e.g., a glucose derivative); imaging of the heart whenthe bioactive group is a fatty acid; imaging of steroid receptor siteswhen the bioactive group is a steroid (e.g., an estrogen for imagingbreast carcinoma); and imaging of sites of infection when the bioactivegroup is a chemotactic peptide with affinity for blood cell types whichlocalize at the site of infection.

[0088] In addition to diagnostic agents, the synthetic method of theinvention also provides stably bound complexes for radiotherapeuticindications, especially where the metal is Re, such as those indicationsdescribed in U.S. Pat. No. 4,871,836. For example, Re complexes whichinclude estradiols can be used in the treatment of breast carcinoma.Also, to the extent that hypoxic tissue is known to be present intumors, Re complexes of the present invention where the bioactive groupis a hypoxia-localizing moiety are suitable for radiotherapy.

[0089] Hypoxia-Localizing Moieties

[0090] Compounds prepared by the synthetic method of the invention willinclude at least one hypoxia-localizing moiety, which specificallylocalizes in hypoxic tissue, e.g. tissue which is deficient in oxygenbut still viable. These compounds may thus be used in diagnostic methodsto obtain information about the state of such tissue.

[0091] Suitable hypoxia-localizing moieties are those which arepreferentially retained in regions of a subject which are hypoxicrelative to the degree of retention in regions which are normoxic. Thegreater the selective localization in hypoxic versus normoxic tissue,the more accurate the information provided. Compounds prepared by themethod of the invention are derivatized with a 2-nitro-imidazolehypoxia-localizing moiety. However, other useful hypoxia localizingmoieties include 4- and 5-nitro-imidazoles, as well as nitrofuran,nitrothiazole and nitrotriazole derivatives. Exemplary groups aredescribed in U.S. Pat. No. 5,608,110.

[0092] Radiopharmaceuticals containing such hypoxia localizing moietieswill display relatively high concentrations in such hypoxic regions,with low concentrations in normoxic and infarcted regions. Complexeswhich concentrate rapidly in hypoxic tissue and which remain stablybound in such tissue over time, while exhibiting a lack of binding andrapid washout from normoxic tissue, are preferred.

[0093] Exemplary diagnostic uses for such complexes, especially wherethe metal complexed is technetium, include imaging of hypoxic tissuepresent under pathological conditions in areas such as the heart, brain,lungs, liver, kidneys or in tumors, or in peripheral vascular diseasessuch as diabetes. In the brain or heart, hypoxia typically followsischemic episodes produced by, for example, arterial occlusions or by acombination of increased demand and insufficient flow. Diagnosticimaging with radiopharmaceuticals of the present invention possessinghypoxia-localizing moieties allows the identification of tissue which isat risk of progressing to infarction, but still salvagable in suchareas.

[0094] Additionally, tumors often have regions within their mass whichare hypoxic. These result when the rapid growth of the tumor is notmatched by the extension of tumor vasculature. Radiopharmaceuticals thatlocalize preferentially within regions of hypoxia may also therefore beused to provide images which are useful in the diagnosis and managementof therapy of tumors. Further, a compound which localizes within thehypoxic region of tumors, and which is labeled with a radionuclide withsuitable α- or β-emissions, may be used for the internal radiotherapy oftumors. Stably bound complexes where Re is the radiometal complexed areparticularly useful for radiotherapeutic indications where hypoxictissue is known to be present in tumors.

[0095] In addition to being useful in imaging hypoxic tissue, thepresent complexes may also be used as blood flow markers, that is, forperfusion imaging. The initial distribution of the novel complexes maybe proportional to blood flow and therefore imaging carried out soonafter administration may be used as an indicator of perfusion. A shorttime later, as the complexes wash out of the normoxic tissue but areretained in the hypoxic tissue, imaging of the hypoxic tissue isrealized.

[0096] Linking Groups

[0097] The linking group(s) (A)_(p) of the compounds made using thesynthetic method of the invention, when present (that is, when p isgreater than zero), may be any one or more moieties which can serve tophysically distance, or otherwise isolate, a bioactive group from theremainder of the compound of Formula I or complex thereof. The presenceof such linking group(s) may be desirable, for example, where abioactive group may be inhibited in its action by the remainder of thecomplex. In considering the various linking groups that may be employed,it is understood that p may be any convenient value depending upon thedesign choice for the desired complex. Preferably, p is ≦20 and is mostpreferably ≦10.

[0098] Preferred linking groups which may be employed alone (where p isone), or together to form a straight or branched chain (where p isgreater than one) and which may be bonded to the remainder of the ligandfrom either end are: —CH₂—, —CHR⁵—, —CR⁵R⁶—, —CH═CH—, —CH═CR⁵—,—CR⁵═CR⁶—, —C═C—, cycloalkyl, cycloalkenyl, aryl (e.g., p-phenylene orhydroxy substituted p-phenylene), heterocyclo, oxygen, sulfur, —C(O)—,—NH—, —HC═N—, —CR⁵═N—, —NR⁵—, or —CS—; wherein R⁵ and R⁶ areindependently selected from alkyl, alkenyl, alkoxy, aryl, 5- or6-membered nitrogen- or oxygen-containing heterocycles, halogen, hydroxyor hydroxyalkyl.

[0099] In the complexes of the present invention, the preferred valuesfor (A)_(p) (bonded to the remainder of the ligand from either end) arealkyl, oxa-alkyl, hydroxyalkyl, hydroxyalkoxy, alkenyl, arylalkyl,arylalkylamide, alkylamide, alkylamine and (alkylamine)alkyl.

[0100] The most preferred values for (A)_(p) are selected from thefollowing (bonded to the remainder of the ligand from either end):—(CH₂)₁₋₅— (especially methyl or ethyl, particularly when bonded to ahypoxia-localizing moiety), —CH₂—CH═CH—CH₂—,—(CH₂)₁₋₂—C(O)—NH—(CH₂)₁₋₃—, —C₆H₅—(CH₂)₁₋₂—, —(CH₂)₁₋₂—CH(OH)—CH₂—,—(CH₂)₂—O—, —CH₂CH(OH)CH₂OCH₂—, —CH₂—C(O)—NH—CH—C₆H₅—, —(A′—O—A″)₁₋₃,and —(A′—NH—A″)₁₋₃; where A′ and A″ are the same or different alkyl oraryl groups and C₆H₅ is p-phenylene.

[0101] Stereoisomers

[0102] All stereoisomers of the compounds and complexes of the presentinvention are contemplated herein, whether alone (that is, substantiallyfree of other isomers), in a mixture of certain stereoisomers (forexample, as a racemate) or in any other mixture thereof. Stereoisomericmixtures may be separated, for example, by use of a suitable chiralcolumn. The R and S isomers of the compounds of Formula I may also beprepared employing chiral starting materials or intermediates as shownbelow.

[0103] Synthetic Scheme for the preparation of S isomers of compounds ofFormula I:

[0104] This method may be used to produce the S isomer of Compound Ia,[(S)-(−)-3,3,9,9-Tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime], starting from(R)-2-Oxyranylmethyl_(—)1-H_isoindole-1,3-(2H)-dione (8) where R and R*in Compound 6a/6b are methyl. This method may also be used to isolateand/or purify the intermediate compound2-{(1R)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione(10).

[0105] Synthetic Scheme for the preparation of R isomers of compounds ofFormula I:

[0106] This method may be used to produce the R isomer of Compound Ia,[(R)-(−)-3,3,9,9-Tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime], starting from(S)-2-Oxyranylmethyl_(—)1-H_isoindole-1,3-(2H)-dione (13)where R and R*in Compound 6a/6b are methyl. This method may also be used to isolateand/or purify the intermediate compound2-{(1S)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione(15).

EXAMPLE

[0107] The following reaction scheme was followed to prepare3,3,9,9-Tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime:

[0108] Synthesis of3,3,9,9-Tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime

[0109] A. Preparation of 2-[2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione

[0110] To a solution of N-(2,3-epoxypropyl)phthalimide (1) (Fluka, 25.0g, 0.123 mol) in ethanol (200 mL), 2-nitroimidazole (2) (Nippon Ghosei,14.5 g, 0.128 mol) and potassium carbonate (1.5 g) were added, and thereaction mixture was heated under reflux for 8 hrs. The reaction mixturewas cooled and the yellow solid obtained was filtered and washed withethanol (2×75 mL). The precipitate was transferred to a one liter beakerand water was added (500 mL). The mixture was stirred for 15 min. Theyellow precipitate was filtered and the solid was washed with water(3×250 mL).2-[2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione(3) was obtained and dried under vacuum. Yield 32.8 g (85%). The productwas pure by proton NMR and HPLC, and was used in the next step withoutfurther purification. A portion (˜2 g) of the solid was recrystallizedfrom methanol. The melting point was 213-214° C.

[0111]¹H NMR (DMSO): δ3.62 (m, 2H, PhthNCH₂CHOH), 4.08 (m, 1H, CHOH),4.32 and 4.63 (m, 2 H, CHOHCH₂N<), 5.54 (d, 1 H, CHOH), 7.15 and 7.68(s, 2 H, imiH), 7.8 (m, 4H, ArH).

[0112] MS: (M+H)⁺=317⁺ (M+Na)⁺=339⁺

[0113] B. Preparation of2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione

[0114] To a slurry of2-[2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione(3) (6.3 g, 0.02 mol) and N-hydroxyphthalimide (4.0 g, 0.0245 mol) inTHF (100 mL), triphenylphosphine (7.5 g, 0.028 mol) was added and themixture was stirred at room temperature for 15 min. The mixture was thencooled to −5° C. and diethylazodicarboxylate (4.95 g, 4.5 mL, 0.028 mol)was added slowly via syringe. The temperature of the reaction mixturerose to 0° C. and the mixture was then stirred at 0° C. for 12 h. Thesolid formed was then filtered, washed with cold THF (−20° C., 100 mL),and dried to obtain 6.0 g (65%) of the crude product.

[0115] HPLC analysis of the crude product obtained indicated thepresence of unreacted N-hydroxyphthalimide as an impurity. The crudeproduct was dissolved in methylene chloride (200 mL) and washed with a10% solution of sodium carbonate (3×75 mL), washed with water and dried(Na₂SO₄). Evaporation of methylene chloride gave 5.4 g (58.7%) of pure2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)-methyl]-ethoxy}isoindoline-1,3-dione(4) which was used in the next step without further purification. Aportion of the2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione(4) was recrystallized from ethyl acetate. The melting point was119-121° C.

[0116]¹HNMR (CDCl₃): δ4.1 (m, 2 H, NCH₂CHO), 4.7 (1 H, NCH₂CHO), 4.88(m, 2 H, CH₂Nphth), 7.25 and 7.27, (2s, 2 H, imiH), 7.7-7.8 (m, 8 H,ArH).

[0117] MS: (M+H)⁺=462.1

[0118] Anal. Calcd. for C₂₂H₁₅N₅O₇: C, 57.27; H, 3.28; N, 15.18; O,24.27% Found: C, 56.81; H, 3.17; N, 15.02%

[0119] C. Preparation of1-[3-amino-2-(aminooxy)propyl]-2-nitro-1H-imidazole

[0120] To a slurry of2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione(4) (2.3 g, 0.005 mol) in methanol (20.0 mL) was added hydrazinemonohydrate (0.625 g, 0.0125 mol) and the mixture was heated at 80° C. Aclear solution was formed in 10 min. and a yellow solid began toseparate (˜20 min). The heating was continued for 3 h and the yellowsolid formed was filtered, washed with methanol, and dried under vacuum.The yellow solid (later identified as the adduct of phthalylhydrazideand the diamine, mp. 214-216° C.) obtained was suspended in hydrochloricacid (1N, 100 mL) and stirred at room temperature for 15 min. The whiteprecipitate formed was filtered and the filter cake was washed withwater (2×10 mL). The filtrate and washings were combined andconcentrated under vacuum to give1-[3-amino-2-(aminooxy)propyl]-2-nitro-1H-imidazole dihydrochloride (5)as a white solid. Absolute ethanol (10 mL) was added to this solid andthe ethanol was removed on a rotary evaporator. This process wasrepeated again and the hydrochloride obtained was dried under vacuum for24 h. This was used in the next step without further purification. Yield1.12 g (82%). A portion of the hydrochloride was crystallized frommethanol ether. The melting point was 143-44° C. (dec).

[0121]¹HNMR (DMSO): δ[3.25 m, 2 H, (CHOCH₂NH₃ ⁺)₂], 4.9 (m, 3, CHOCH₂imi), 7.15 and 7.72(s, 2 H, imiH), 8.5 (bs, 6H, NH₃ ⁺).

[0122] MS: (M+H)⁺=202

[0123] D. Preparation of 3-chloro-3-methyl-2-nitrosobutane

[0124] 3-chloro-3-methyl-2-nitrosobutane was prepared according toNowotnik et al., European Patent No. 0179608 A2 (1986).

[0125] A 250 mL 3-necked flask fitted with a mechanical stirrer, adropping funnel, and a thermometer was charged with 2-methyl-2-butene(8)(27.5 mL, 18.2 g, 0.259 mol) and isoamyl nitrite (32.5 mL, 28.3 g,0.242 mol). The mixture was then cooled to −15° C. and concentrated HCl(27 mL, 0.329 mol) was added dropwise over a period of 30 minmaintaining the temperature at −10° C.-5° C. The light blue slurry wasstirred at −10° C.˜-5° C. for an additional 30 min. The wet product wasdissolved in petroleum ether (bp 30-60° C., 150 mL). The bottom aqueouslayer was removed and the organic layer was dried (Na₂SO₄). Thepetroleum ether solution was filtered and cooled to −50° C. withoccasional stirring, and the white crystalline solid formed wascollected by filtration, washed with cold (−50° C.) petroleum ether anddried under vacuum at RT overnight. Yield 18.4 g (56%). mp. 72-73° C.,lit. 72.5-74° C.

[0126]¹HNMR (CDCl₃): δ1.50 [d, 3 H, CHNOCH₃)], 1.65 and 1.69 [2 s, 6 H,C(CH₃)₂], 5.97 (q, 1 H, CHNO)

[0127] E. Preparation of3,3,9,9-tetramethyl-6-[(2-nitro-1H-imidazol-1-yl)methyl]-5-oxa-4,8-diazaundecane-2,10-dionedioxime

[0128] In a nitrogen-flushed, 50-mL, round-bottomed flask equipped witha magnetic stirrer was charged1-[3-amino-2-(aminooxy)propyl]-2-nitro-1H-imidazole dihydrochloride (5)(1.37 g, 0.005 mol) and acetonitrile (15.0 mL). To the white suspension,diisopropylethylamine (4.29 g, 5.95 mL, 0.033 mol) was added.3-chloro-3-methyl-2-nitrosobutane (6) (1.5 g, 0.011 mol) was then addedto this mixture and the mixture stirred at room temperature. Theprogress of the reaction was monitored by HPLC. An aliquot of thereaction mixture was withdrawn after 30 min. HPLC analysis indicated thedisappearance of the dihydrochloride and the formation of the mono oximeat t_(R) 14.47 (80.5%) min, and the product (17%) t_(R)=22.02 min. After6 hr of the elapsed reaction time the percentage of intermediate monooxime at t_(R)=14 47 (confirmed by LC mass spec) had changed (45.9%).Using HPLC for monitoring the reaction progress, additionalchloro-3-methyl-2-nitrosobutane (0.3 g in 2×0.15 g portions) was addeduntil the reaction was judged complete (disappearance of the mono oximeat t_(R)=14.47 min). Acetonitrile was then removed on a rotaryevaporator and the thick oil obtained was basified with saturatedpotassium carbonate solution (2.5 g, in 25 mL of water). The light greenoil obtained was extracted with ethyl acetate and dried (Na₂SO₄). Ethylacetate was removed on a rotary evaporator and the oil obtained wasdissolved in acetonitrile (5.0 mL) and the acetonitrile was removed byrotary evaporation. This process was repeated again and the viscous oilobtained was dried under vacuum for 24 h to give a foamy solid. Thefoamy solid was dissolved in acetonitrile (7.0 mL) and left at roomtemperature for 2 h. The dioxime (7) that formed was filtered andrecrystallized from acetonitrile. Yield: 1.2 g (60.%). mp. 170-71° C.

[0129]¹HNMR (DMSO-d₆): δ0.96 and 1.11 [s, 12 H, C(CH₃)₂], 1.65 (s, 6 H,CH₃), 2.30 (m, 2H, HNCH₂CHOH), 3.80 (m, 1 H, CHO), 4.5 (m, 2 H,CHOHCH₂N<), 7.15 and 7.59 (s, 2H, imiH) 10.43 (s, 2H, NOH).

[0130] MS: (M+H)⁺=400.2

[0131] Anal. Calcd. for C₁₆H₂₉N₇O₅: C, 48.11; H, 7.32; N, 24.55; O,20.03%. Found C, 48.47; H, 7.11; N, 24.59.

[0132] Other Embodiments

[0133] From the foregoing description, it will be apparent thatvariations and modifications may be made to the invention describedherein to adopt it to various usages and conditions.

[0134] Incorporation by Reference

[0135] All publications, patents, and patent applications mentioned inthis specification are herein incorporated by reference to the sameextent as if each independent publication, patent, or patent applicationwas specifically and individually indicated to be incorporated byreference.

What is claimed is:
 1. A compound having the structure of Formula II:


2. The compound of claim 1, having the structure:


3. The compound of claim 1, having the structure:


4. A method of synthesizing a compound of claim 1 having the structureFormula II:

the method comprising the steps of: (i) contactingN-(2,3-epoxypropyl)phthalinide with 2-nitroimidazole to obtain2-[2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione;and (ii) contacting the product of (i) with N-hydroxyphthalimide toobtain2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione.5. The method of claim 4, wherein the compound has the structure

the method comprising the steps of (i) contacting(R)-2-Oxyranylmethyl_(—)1-H_isoindole-1,3-(2H)-dione with2-nitroimidazole to obtain2-[(2S)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione;and (ii) contacting the2-[(2S)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dionewith N-hydroxyphthalimide to obtain2-{(1R)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione.6. The method of claim 4, wherein the compound has the structure

the method comprising the steps of: (i)(S)-2-Oxyranylmethyl_(—)1-H_isoindole-1,3-(2H)-dione with2-nitroimidazole to obtain 2-[(2R)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H -isoindole-1,3(2H)-dione; and (ii) contactingthe 2-[(2R)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione with N-hydroxyphthalimide to obtain2-{(1S)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione.7. A synthetic method comprising the steps of: (i) contacting2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione:

 with hydrazine, to obtain 1-(3-amino-2-(aminooxy)propyl)-2-nitro-1H-imidazole dihydrochloride; and (ii) contacting the product of (i) witha compound having the structure IIIa or IIIb or a mixture thereof:

where X is halogen and all R and R* groups are independently: (i) R²;(ii) halogen; (iii) —OR²; (iv) —C(O)—OR²; (v) —C(O)—N(R²)₂; (vi)—N(R²)₂; (vii) -alkyl-C(O)—OR²; (viii) -alkyl-C(O)—N(R²)₂; (ix)-alkyl-N(R²)₂; (x) -aryl-C(O)—OR²; (xi) -aryl-C(O)—N(R²)₂; (xii)-aryl-N(R²)₂; (xiii) acyl; (xiv) acyloxy; (xv) heterocyclo; (xvi)hydroxyalkyl; (xvii) —SO₂—R²; (xviii) -alkyl-SO₂—R²; (xix) —(A)_(p)—R³,where A is a linking group, p is 0 or a positive integer, and R³ is abioactive moiety; or (xx) two R groups, or an R group and an R* group,taken together with the one or more atoms to which they are bonded, forma saturated or unsaturated, spiro or fused, carbocyclic (such as fused1,2-phenyl) or heterocyclic ring which may be unsubstituted orsubstituted by one or more groups selected from the groups (i) to (xix)above; with the proviso that a carbon atom bearing an R group is notdirectly bonded to more than one heteroatom; and R² is independentlyhydrogen, alkyl, alkenyl, alkynyl, or aryl.
 8. The method of claim 7,wherein R is methyl.
 9. The method of claim 7, wherein R* is methyl. 10.The method of claim 7, wherein R is methyl and R* is methyl.
 11. Themethod of claim 7, wherein X is selected from Cl, Br, and I.
 12. Themethod of claim 7, wherein the compound having the structure IIIa orIIIb is 3-chloro-3-methyl-2-nitrosobutane.
 13. The method of claim 7,further comprising the step of contacting2-[2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dionewith N-hydroxyphthalimide to obtain the2-{2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione.14. The method of claim 13, further comprising the step of contactingN-(2,3-epoxypropyl)phthalimide with 2-nitroimidazole to obtain the2-[2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione.15. The method of claim 14, wherein R is methyl.
 16. The method of claim14, wherein R* is methyl.
 17. The method of claim 14, wherein R ismethyl and R* is methyl.
 18. The method of claim 14, wherein X isselected from Cl, Br, and I.
 19. The method of claim 14, wherein thecompound having the structure IIIa or IIIb is3-chloro-3-methyl-2-nitrosobutane.
 20. The method of claim 7, furthercomprising the step of contacting2-[(2S)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione:

with N-hydroxyphthalimide to obtain2-{(1R)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione:


21. The method of claim 20, further comprising the step of contacting(R)-2-Oxyranylmethyl_(—)1-H_isoindole-1,3-(2H)-dione with2-nitroimidazole to obtain2-[(2S)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione:


22. The method of claim 21, wherein R is methyl.
 23. The method of claim21, wherein R* is methyl.
 24. The method of claim 21, wherein R ismethyl and R* is methyl.
 25. The method of claim 21, wherein X isselected from Cl, Br, and I.
 26. The method of claim 21, wherein thecompound having the structure IIIa or IIIb is3-chloro-3-methyl-2-nitrosobutane.
 27. The method of claim 7, furthercomprising the step of contacting2-[(2R)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione:

with N-hydroxyphthalimide to obtain2-{(1S)-2-(1,3-dioxoisoindolin-2-yl)-1-[(2-nitroimidazolyl)methyl]ethoxy}isoindoline-1,3-dione:


28. The method of claim 27, further comprising the step of contacting(S)-2-Oxyranylmethyl_(—)1-H_isoindole-1,3-(2H)-dione with2-nitroimidazole to obtain2-[(2R)-2-hydroxy-2-(2-nitro-1H-imidazol-1-yl)ethyl]-1H-isoindole-1,3(2H)-dione:


29. The method of claim 28, wherein R is methyl.
 30. The method of claim28, wherein R* is methyl.
 31. The method of claim 28, wherein R ismethyl and R* is methyl.
 32. The method of claim 28, wherein X isselected from Cl, Br, and I.
 33. The method of claim 28, wherein thecompound having the structure IIIa or IIIb is3-chloro-3-methyl-2-nitrosobutane.